Brakes

ABSTRACT

In agricultural trailers hydraulic brakes which are actuated by depressing the brake pedal of the towing tractor, it has been found that there is a tendency for a poppet valve to vibrate as oil passes through it. This invention provides a throttling valve in series with the poppet valve which damps such vibrations.

O Unlted States Patent 1 I 1 3,806,201 Montanari Apr. 23, 1974 [54] BRAKES 2,161,642 6/1939 Stroup 303/7 [75] Inventor: Marc Montanari, F esnes, rance 2,626,629 l/l953 Mueller et al. 251/120 X [73] Assignee: Massey-Ferguson Service NV,

Curaco, Netherlands Antilles Primary Examiner Mi1ton Buchler 22 Filed: Oct- 5 1972 ASSiSldfll ExaminerPaul E. Sauberer Attorney, Agent, or Firm-Robert L. Farris [21] Appl. No.: 295,332

[30] Foreign Application Priority Data Oct. 14, 1971 Great Britain 47757/71 [57] ABSTRACT [52] US. Cl. 303/7, 303/84 R 51 im. c1 B60t 13/10 agnculwral allers hydraullc brakes Whlch are w [58] Field of Search 251/120, 118, 211- mated by depressing the brake Pedal of the towing C 21 F 84 A 7 R tractor, it has been found that there iS a tendency for a poppet valve to vibrate as oil passes through it. This invention provides a throttling valve in series with the 56] References Cited poppet valve which damps such vibrations.

UNITED STATES PATENTS 3,269,781 8/1966 Van House 303/84 R 2 Claims, 3 Drawing Figures BRAKES This invention relates to apparatus for controlling supply of hydraulic fluid to a hydraulically actuable brake on a trailer.

In co-pending application U.S. Ser. No. 096194 filed Dec. 8, 1970 now U.S. Pat. 3,690,734 there is described and claimed a braking apparatus for controlling supply of hydraulic fluid to a trailer hydraulic brake, the apparatus comprising a pilot operated distributing valve having an inlet for hydraulic fluid from a hydraulic fluid pressure supply and an outlet for the passage of hydraulic fluid fromthe supply means to a hydraulic brake, conduit means in communication with a pilot fluid chamber of the distributing valve and adapted to convey pilot fluid from a source to discharge through a discharge control valve adapted to vary pilot fluid pressure in accordance with variation in force applied to the tractor brake pedal.

The pedal operated control valve has displayed an undesirable characteristic in that it has tended to chatter" or produce pressure fluctuation during operation, especially where a force operating the valve is applied through an agency having some degree of resilience or yieldability.

An object of the present invention is-to provide a fluid flow control valve wherein the said undesirable characteristic is obviated or mitigated.

The invention presents as a solution to the above problem a fluid flow control valve incorporating at least two sets of flow restricting elements which are arranged in series with respect to flow through the valve, the elements of a first of the sets defining a first 'flow restriction which is variable in proportion to a force operating the valve, the elements of the second of the sets defining a second flow restriction which remains substantially constant and defines a flow clamping orifice while the elements of the first set are in operation. The elements of the second set are preferably upstream with respect to the first set of elements.

Embodiments of the invention will now be described by way of example with reference to the drawings in which:

FIG. l is a sectional elevation of a control valve in a condition allowing free flow of fluid through the valve;

FIG. is a sectional elevation corresponding with FIG. 1 but showing the valve in a condition in which flow of fluid through the valve is restricted; and

FIG. 3 is a sectional elevation illustrating a control valve such as is described in co-pending U.S. Pat. application Ser. No. 096194, now U.S. Pat. No. 3,690,734 but incorporating the present invention by way of modification and improvement.

In FIGS. 1 and 2 of the drawings, a flow control valve consists of a hollow valve body 1 provided with an inlet port 2 and an outlet port 3. A valve spool 4 is slidably supported by the valve body and cooperates with seals indicated at5 and 6. The valve body 1 supports an insert 7 co-axial with the valve spool 4. The insert 7 is arranged between the inlet and outlet ports 2 and 3 so that fluid flows through the insert during the passage of fluid through the valve.

The valve spool 4 and the insert 7 are formed so as to define two sets of flow-restricting elements which are arranged in series with respect to the direction of fluid flow through the valve. A first set of flowrestricting elements is constituted by a mitre valve indicated generally at 8 and consisting of a tapered shoulder 9 on valve spool 4 and a tapered seating 10 on the insert 7. A second set of flow-restricting elements is constituted by a cylindrical land 11 on the valve spool 4 and a cylindrical bore 12 in the insert 7. The diameter of the cylindrical land 11 is slightly smaller than the diameter of the cylindrical bore 12 so that the land 11 may enter the bore 12 and so define an annular metering orifice through which fluid must pass. It can be seen in FIGS. 1 and 2 that the second set of flow-restricting elements is upstream of the first set, that is to say the annular metering orifice defined by land 11 and bore 12 is upstream of the mitre valve 8. A spring (not shown) may be provided and arranged to act between the valve body 1 and the valve spool 4 so as to urge the valve spool 4 to the left in FIGS. 1 and 2 thus placing the valve in a fully open condition in which the mitre valve 8 is open and the cylindrical land 11 is clear of the bore 12.

With the valve in the condition shown in FIG. 1 fluid under pressure admitted through the inlet port 2 may flow through the valve and be discharged through the outlet port 3 with no significant pressure drop appearing across the inlet and outlet ports.

Before considering the condition of the valve illustrated in FIG. 2 the following is mentioned by way of explanation. Ignoring'for the moment the presence of the cylindrical land 11' and the bore 12, it can be appreciated that while fluid from a pressure course is flowing through the valve, movement of the valve spool 4 so as to tend to close the mitre valve 8 will immediately re sult in the establishing of a pressure drop across the valve. It can be seen that the, increase in pressure on the inlet side will act so as to tend to move the valve spool 4 to the left, that'is the increase in pressure on the inlet side will tend to open the mitre valve 8. If a force operating the valve spool 4 is applied through an agency having some degree of resilience of yieldability, it can be seen that undercertain conditions of fluid pressure and fluid flow rate there would develop a tendency for the valve spool 4 to chatter or produce pressure fluctuations due to the fact that the establishment of a fluid pressure increase on the inlet side of the valve would tend to open the mitre valve 8 by virtue of the resilient or yieldable nature of the agency through which the operating force is applied. Upon a slight opening of the mitre valve 8 a consequent reduction in fluid pressure on the inlet side of the valve would allow the force op erating the valve to tend to close the mitre valve 8. Under certain conditions, these events would occur cyclically and so produce the pressure fluctuations mentioned above. These pressure fluctuations produce an undesirable characteristic of vibration which can affect proper operation of a hydraulic system of which the valve'may form part. Also, the vibration may be transmitted to whatever means are employed to actuate the valve spool. Where these actuating means are manual for example as in a vehicle braking system, an objectionable cyclic movement may be felt.

In FIG. 1 it can be seen that the mitre valve 8 is open and that the cylindrical land 1] lies outside the bore 12 so that there is a free passage for the flow of fluid through the valve in the direction of the arrows shown in the drawings. In this condition, there is little or no pressure drop across the valve. In FIG. 2, a force F acts on the valve spool 4 in the direction indicated at F so plication Ser.

as to establish a restriction at the mitre valve 8 to flow of fluid through the valve. At the same time, the cylindrical land 11 has moved to a position in which it occupies the greater part of the bore 12 so defining an annular metering orifice between the land 11 and the bore 12. A greater or lesser degree of magnitude of the force F producing a greater or lesser degree of restriction at the mitre valve 8 will be accompanied by no significant change in the metering effect of the metering orifice between the land 11 and the bore 12. That is to say, while the elements of the mitre valve 8 mutually cooperate to define a flow restriction which is variable by means of small movements of the valve spool 4, the flow restriction constituted by the metering orifice between the land 1 l and the bore 12 remains substantially constant and provides fluid damping sufficient to eliminate or substantially to reduce any tendency for the valve spool to chatter. Thus, the control valve described above is operable between the condition allowing free fluid flow with little or no pressure drop across the valve, and a condition of variable restrictive effect during which damping is automatically introduced to a degree sufficient to obviate or mitigate pressure fluctuations across the valve.

In FIG. 3 those reference numerals have the suffix P correspond with the reference numerals used in FIG. 1 of the drawings filed with the specification of Pat. ap-

No. 096194, now U.S. Pat. No. 3,690,734. Reference should be made to the disclosure in the said patent application whereby it will be seen that the valve shown in FIG. 3 of the present application constitutes an improvement of or modification to the pilot fluid pressure control valve described in the earlier application Ser. No. 096194. In the earlier case, the valve P14 constitutes part of a linkage in a vehicle braking system. In accordance with the present invention, the valve element or spool P23 is provided with a cylindrical land 11A corresponding with the cylindrical Y land 11 in FIGS. 1 and 2 of the present application.

Also the valve insert P33 is provided with a bore 12A which corresponds with the bore 12 in FIGS. 1 and 2 of the present application. The land 11A and the bore 12A constitute the elements of a flow restriction as described with reference to FIGS. 1 and 2 of the present application.

In modifications of the embodiments described above, the land 11 or 11A and the bore 12 or 12A is replaced by alternative elements capable of mutual cooperation so as to define a flow restriction which will remain substantially constant despite relative movement between the elements after initial restriction has been established. For example the land 11 or 11A and the bore 12 or 12A need not necessarily be cylindrical nor need they necessarily be of the same crosssectional shape. It is sufficient that relative movement of the two elements concerned can bring them together so as to constitute a flow restriction of a predetermined size and which will present a substantially constant flow restriction during subsequent operation of the valve so as to vary the restriction between the elements of the other flow restriction.

I claim:

1. In combination with a tractor having a brake and supply means for providing hydraulic fluid under pressure for auxiliary services, apparatus for controlling supply of hydraulic fluid to a trailer hydraulic brake comprising: a pilot-operated distributing valve having an inlet for hydraulic fluid from the supply means, a pilot fluid chamber, a pilot fluid source and an outlet for the passage of hydraulic fluid from the supply means to the trailer hydraulic brake, a discharge control valve, and conduit means in communication with the pilot fluid chamber for conveyingpilot fluid from the pilot fluid source through the discharge control valve to vary'pilot fluid pressure inaccordance with variation in force applied to actuate the tractor brake, characterized in that said discharge control valve incorporates sets of flow-restricting elements, the sets being arranged in series with the first set downstream from the second set with respect to the fluid flow through the valve, the elements of a first of the sets which comprise a mitre valve with a spool and a seat being mutually co-operable so as to define a first flow restriction which is variable in proportion to a force operating the valve, the elements of a second of the sets including a land on the spool for the first of the sets of flowrestricting elements and a bore that are mutually cooperable so as to define a second flow restriction which remain substantially constant during co-operation of the elements of the first set for limiting the passage of hydraulic fluid, and said land moving clear of the bore of the second of the sets of flow restricting elements when the first of the sets of flow restricting elements is in a fully open condition.

2. Apparatus according to claim 1 wherein the elements of the second set are mutually co-operable was to define an annular metering orifice. 

1. In combination with a tractor having a brake and supply means for providing hydraulic fluid under pressure for auxiliary services, apparatus for controlling supply of hydraulic fluid to a trailer hydraulic brake comprising: a pilot-operated distributing valve having an inlet for hydraulic fluid from the supply means, a pilot fluid chamber, a pilot fluid source and an outlet for the passage of hydraulic fluid from the supply means to the trailer hydraulic brake, a discharge control valve, and conduit means in communication with the pilot fluid chamber for conveying pilot fluid from the pilot fluid source through the discharge control valve to vary pilot fluid pressure in accordance with variation in force applied to actuate the tractor brake, characterized in that said discharge control valve incorporates sets of flow-restricting elements, the sets being arranged in series with the first set downstream from the secoNd set with respect to the fluid flow through the valve, the elements of a first of the sets which comprise a mitre valve with a spool and a seat being mutually co-operable so as to define a first flow restriction which is variable in proportion to a force operating the valve, the elements of a second of the sets including a land on the spool for the first of the sets of flowrestricting elements and a bore that are mutually co-operable so as to define a second flow restriction which remain substantially constant during co-operation of the elements of the first set for limiting the passage of hydraulic fluid, and said land moving clear of the bore of the second of the sets of flow restricting elements when the first of the sets of flow restricting elements is in a fully open condition.
 2. Apparatus according to claim 1 wherein the elements of the second set are mutually co-operable so as to define an annular metering orifice. 